In recent years, an article management system using an RFID (Radio Frequency Identification) tag has been used for the purpose of, for example, effective inventory management of articles (for example, Patent Literature 1).
As an article presence/absence detection system, for example, a technique has been proposed in which an interference unit that interferes with electromagnetic induction is attached to a bottom portion of each article and each article is placed immediately above an RFID tag. In this technique, an identification signal of each RFID tag is read by electromagnetic induction from a coil unit that is provided immediately below the corresponding RFID tag. At this time, the presence or absence of an article can be detected based on the presence or absence of the interference unit, i.e., based on a variation in the ratio of reading of the RFID tag. Accordingly, this article presence/absence detection system can be structured at a lower cost than a system in which RFID tags are attached to all articles by attaching the interference unit to a bottom portion of each of the articles. In a case where a relatively large metal body, such as a beverage can, is used as an article, the presence or absence of the article can be detected without attaching the interference unit to the article. This is because the ratio of reading of each RFID tag varies.